1. Field of the Invention
This invention is a water based machining fluid with a synergistic rust inhibiting combination of an amphoteric imidazole derivative, a free amine and amine salts of dicarboxylic acids.
2. Description of the Prior Art
Aqueous systems have been preferred for many machine applications which are subject to high heat or sparks. Such applications include hydraulic fluids for use in systems involving a high risk of fire, and in quenchants used to cool heated metals during various metal working processes where the hot metals can ignite hydrocarbon based quenchants. However, aqueous systems are corrosive toward metal, particularly ferrous metal.
In a previously used aqueous system which is non corroding to metals, an inorganic nitrite, such as sodium nitrite, was used to impart improved corrosion inhibition to the aqueous system. However, nitrites are somewhat toxic and in recent years there has been a movement toward the removal of nitrites and the replacement with other materials to impart corrosion inhibition to the aqueous system.
U.S. Pat. Nos. 4,450,088 and 4,452,758 describe aqueous antifreeze compositions comprising 2-heptyl-1-ethoxypropionic acid imidazoline, sodium salt and triethanolamine.